Fix missing parens in reprinted output

lib/fast-path.ts

@@ -324,9 +324,6 @@ FPp.needsParens = function (assumeExpressionContext) {
   }
 
   const parent = this.getParentNode();
-  if (!parent) {
-    return false;
-  }
 
   const name = this.getName();
 
@@ -347,13 +344,16 @@ FPp.needsParens = function (assumeExpressionContext) {
     return false;
   }
 
-  if (
-    parent.type === "ParenthesizedExpression" ||
-    (node.extra && node.extra.parenthesized)
-  ) {
+  if (parent && parent.type === "ParenthesizedExpression") {
     return false;
   }
 
+  if (node.extra && node.extra.parenthesized) {
+    return true;
+  }
+
+  if (!parent) return false;
+
   switch (node.type) {
     case "UnaryExpression":
     case "SpreadElement":

lib/printer.ts

@@ -196,14 +196,14 @@ function genericPrint(path: any, config: any, options: any, printPath: any) {
     return linesWithoutParens;
   }
 
-  let shouldAddParens = node.extra ? node.extra.parenthesized : false;
+  let shouldAddParens = false;
   const decoratorsLines = printDecorators(path, printPath);
 
   if (decoratorsLines.isEmpty()) {
     // Nodes with decorators can't have parentheses, so we can avoid
     // computing path.needsParens() except in this case.
     if (!options.avoidRootParens) {
-      shouldAddParens = shouldAddParens || path.needsParens();
+      shouldAddParens = path.needsParens();
     }
   } else {
     parts.push(decoratorsLines);

parsers/babel-ts.ts

@@ -0,0 +1,10 @@
+import { parser } from "./babel";
+import getBabelOptions, { Overrides } from "./_babel_options";
+
+export { parser };
+
+export function parse(source: string, options?: Overrides) {
+  const babelOptions = getBabelOptions(options);
+  babelOptions.plugins.push("jsx", "typescript");
+  return parser.parse(source, babelOptions);
+}

test/parens-babylon.ts → test/parens-extra.ts

@@ -1,7 +1,9 @@
 import assert from "assert";
+// the babel parser denotes decorative parens with extra.parenthesized
 import * as babylon from "@babel/parser";
 import { parse as recastParse } from "../lib/parser";
 import { Printer } from "../lib/printer";
+import * as parser from "../parsers/babel-ts";
 import * as types from "ast-types";
 
 const printer = new Printer();
@@ -12,23 +14,20 @@ function parseExpression(expr: any) {
   return n.ExpressionStatement.check(ast) ? ast.expression : ast;
 }
 
-const parse = (expr: string) =>
-  recastParse(expr, {
-    parser: babylon,
-  });
+const parse = (expr: string) => recastParse(expr, { parser });
 
 function check(expr: string) {
   const ast = parse(expr);
 
   const reprinted = printer.print(ast).code;
-  assert.strictEqual(reprinted, expr);
+  assert.strictEqual(expr, reprinted);
 
   const expressionAst = parseExpression(expr);
   const generic = printer.printGenerically(expressionAst).code;
   types.astNodesAreEquivalent.assert(expressionAst, parseExpression(generic));
 }
 
-describe("babylon parens", function () {
+describe("parens from node.extra.parenthesized", function () {
   it("AwaitExpression", function () {
     check("async () => ({...(await obj)})");
     check("(async function* () { yield await foo })");
@@ -55,4 +54,20 @@ describe("babylon parens", function () {
 
     assert.strictEqual(printer.print(ast).code, "(1).foo");
   });
+
+  it("prints top level parens for an expression ast", function () {
+    check("(() => {})()");
+    check("(function () {} ())");
+  });
+
+  describe("reprinter", function () {
+    it("preserves necessary parens", function () {
+      const ast = parse("() => ({ prop: true })");
+      const expr = ast.program.body[0].expression;
+
+      expr.body.properties = [];
+
+      assert.strictEqual(printer.print(ast).code, "() => ({})");
+    });
+  });
 });

test/run.ts

@@ -5,6 +5,7 @@ import "./identity";
 import "./jsx";
 import "./lines";
 import "./mapping";
+import "./parens-extra";
 import "./parens";
 import "./parser";
 import "./patcher";

test/typescript.ts

@@ -5,10 +5,6 @@ import * as recast from "../main";
 import * as types from "ast-types";
 import { EOL as eol } from "os";
 import * as parser from "../parsers/typescript";
-import { Printer } from "../lib/printer";
-
-const { namedTypes: n } = types;
-const printer = new Printer();
 
 // Babel 7 no longer supports Node 4 or 5.
 const nodeMajorVersion = parseInt(process.versions.node, 10);
@@ -311,34 +307,6 @@ const nodeMajorVersion = parseInt(process.versions.node, 10);
       "type Alpha = Color.a;",
     ]);
   });
-
-  it("parens", function () {
-    function parseExpression(expr: any) {
-      let ast: any = parser.parse(expr).program;
-      n.Program.assert(ast);
-      ast = ast.body[0];
-      return n.ExpressionStatement.check(ast) ? ast.expression : ast;
-    }
-
-    const parse = (expr: string) => recast.parse(expr, { parser });
-
-    function check(expr: string) {
-      const ast = parse(expr);
-
-      const reprinted = recast.print(ast).code;
-      assert.strictEqual(reprinted, expr);
-
-      const expressionAst = parseExpression(expr);
-      const generic = printer.printGenerically(expressionAst).code;
-      types.astNodesAreEquivalent.assert(
-        expressionAst,
-        parseExpression(generic),
-      );
-    }
-
-    check("(() => {}) as void");
-    check("(function () {} as void)");
-  });
 });
 
 testReprinting(